3 available mechanisms: by public key, by host name, and by certificate subject name.
In the former method, chain of trust verification is not performed.
The CA certificate files are looked for under <spice-config-dir>/spice_truststore.pem
windows <spice-config-dir>=%APPDATA%\spicec\
linux <spice-config-dir>=$HOME/.spicec
Additional changes that were required for the feature:
1) focusing on the pointed window in full screen mode
2) In X11 - handling events that occur during keyboard ungrabbing
3) In X11 - handling Leave/Enter Notify events that occur during keyboard grabbing/ungrabbing
4) In X11 - fix for focus events that are handled in the wrong order (happens when
focus events occur during grabbing the keyboard)
5) In X11 - ignoring key release events during key holding
6) In Windows - synchronizing keyboard release events that occured during a modal loop
The process loop is responsible for: 1) waiting for events 2) timers 3) events queue for
actions that should be performed in the context of the thread and are pushed from other threads.
The benefits:
1) remove duplicity: till now, there was one implementaion of events loop for the channels and
another one for the main thread.
2) timers can be executed on each thread and not only on the main thread.
3) events can be pushed to each thread and not only to the main thread.
In this commit, only the main thread was modified to use the new process loop.
